Nucleated vesicular film



Nov. 28, 1967 w, m s 3,355,295

NUCLEATED VESICULAR FILM Filed Feb. 11, 1964 X t o; E Q

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EXPOSURE (LOG E L06.

.SPECULAR pews/Tr EXPOSURE (L06 E, LOG 1 WILL/AM J. PRIEST INVENTOR ATTORNEYS United States Patent 3,355,295 NUCLEATED VESICULAR FILM 'William J. Priest, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed Feb. 11, 1964, Ser. No. 344,071 3 Claims. (Cl. 96-91) ABSTRACT OF THE DISCLOSURE This invention relates to vesicular photographic elements, and more particularly to vesicular photographic .elements having improved speed and image quality.

Itis known that certain light-sensitive gas-releasing materials dissolved or dispersed in matrices of suitable stiffness and suitably low permeability to gases, and coated on a support, may be utilized for the preparation of images frequently referred to as vesicular images. In .these materials, the image effect is due to the scattering of light by groups of very small bubbles in photolytically generated gas retained in the matrices. Formation of .these vesicular images usually involves irradiation through a design followed by brief application of heat. 'While ordinary vesicular photographic elements provide satisfactory results in many respects, it is frequently .desirable to improve the speed and image quality thereof. This has previously been accomplished by providing nuclei for bubble formation in the coatings. In one method of nucleation, various treatments are given the film after coating the light-sensitive material and binder on a support, and after curing the coating. However, while some of the techniques of nucleating after the coating of the light sensitive material has provided good results, it would be highly desirable to obtain nucleation during .the course of the coating operation without having to resort to subsequent treatments.

Previous methods of providing nucleated vesicular photographic elements without resorting to subsequent treatments after coating have been subject to various disadvantages. For example, salts of long-chain fatty acids in the form of finely divided powders have been incorporated into vesicular coating compositions, but this method of nucleation suffers from the disadvantage that the particle size of such additives cannot be made small enough to prevent the unwanted scattering of light. Certain other salts which have been incorporated in the coating composition, and which do have a sufliciently small particle size, have been objectionable since they render the light-sensitive vesicular coating subject to the effects of high relative humidity. It therefore appears desirable to provide vesicular photographic elements which have increased speed and image quality, and are not subject to the disadvantages of vesicular films nucleated in accordance with the prior art.

One object of my invention is to provide vesicular photographic elements having improved speed and image quality. Another object of my invention is to provide nucleated vesicular photographic elements, which elements are substantially free from unwanted scattering of light and the effects of high relative humidity. A further object of my invention is to provide a method of coating light-sensitive gas-releasing materials dissolved in suitable after which the specular optical density was less than -30 seconds through a graded density wedge in which polymeric binders onto a suitable support whereby minute inhomogeneities are created in the polymeric binder. Other objects of my invention will appear herein.

These and other objects of my invention are accomplished by vesicular photographic elements comprising a support having coated thereon a continuous phase thermoplastic polymeric binder having a discontinuous phase wax dispersion therein, which coating also contains a compound which releases gas imagewise upon exposure to radiation.

I have found that vesicular photographic elementsin accordance with my invention may be prepared by coating the polymeric binder, light-sensitive gas-forming compound and wax from a solvent solution comprising a first solvent in which the polymeric binder and gas-forming compound have good solubility, and a second solvent, of less volatility than the first solvent, which is a poor solvent for the polymeric binder but which is a good solvent for the wax. When such coating compositions are coated upon a support, a phase separation occurs prior to evaporation of all the solvents, and minute inhomogeneities are created in the coating which serve as nuclei for bubble formation, thereby increasing speed and image quality of the material.

My invention will be further illustrated in the following example which shows a vesicular photographic element and the method of its preparation in accordance with the invention.

Example 1 A solution was made consisting of 2.7 grams vinylidene chloride acrylonitrile copolymer (about parts by weight vinylidene chloride and about 20 parts by weight acrylonitrile), .3 gram poly(methyl methacrylate) (Du Pont Lucite 41) and 0.3 gram l-hydroxy-Z-carbazidonaphthalene (light-sensitive gas-forming compound) in 7 grams methyl ethyl ketone. This solution was combined with a mixture of .09 gram of a hydrogenated oil wax' (Archer Daniel Midlands Hydrofol Glycerides 200) and 0.1 gram of a 25% aqueous solution of sodium lauryl sulfate (surfactant) in .4 gram n-amyl alcohol. The mixture of the two solutions was heated slightly to keep the solids in solution. The resulting solution was then knife coated (.006 inch gap) on poly(ethylene terephthalate) film base supported on a coating block heated to about 35 C. During solvent loss, a uniform haze appeared having an optical density about .3 (specular). The coating was then heated for 10 minutes in an air oven at C. .1. for the density increments amounted to log 2. The light source for the exposure was an ultraviolet fluorescent tube of 8 .The coated film strip thus obtained was exposed watts, and the specimen distance was 3.3 cm. from the line of center of the tube. After exposure, the sample was developed in boiling water for 23 seconds. Specular densities were read for each step of the image at 24 collection cone angle. These tests were conducted with both fresh nucleated samples and nucleated samples after againg two weeks at 25 C. and 50% relative humidity. The results are shown in FIG. 1, curves 1a and 2a respectively.

The following example shows the results achieved with a vesicular photographic element which is not nucleated in accordance with the invention, and clearly points out the improvements in speed achieved in accordance with applicants invention.

Example 2 The procedure of Example 1 was followed except that the wax and surfactant were omitted from the coating composition. The haze which formed during coating vanished during the baking operation. Two strips thus prepared were tested fresh and after aging two weeks at 25 C. and 50% relative humidity in the manner of the vesicular photographic elements obtained in accordance with Example 1. The sensitometric properties of these samples are shown in FIG. 1, curves 1B and 2B respectively.

The following examples demonstrate vesicular photographic elements similar to those obtained in Example 1, with the exception that various waxes are substituted for the hydrogenated oil wax employed therein.

Example 3 The procedure of Example 1 was followed except that carnauba wax was substituted for the wax of Example 1. The element thus obtained reproduced two steps more than its control.

Example 4 The procedure of Example 1 was followed except that the wax employed was Opalwax, a hydrogenated castor oil wax. The element thus obtained reproduced two steps more than its control.

Example 5 The procedure of Example 1 was followed except that the wax employed was l8-pentatriaeontanone (Stearone). The photographic element obtained reproduced two steps more than its control.

Example 6 The procedure of Example 1 was followed except that a white synthetic wax, sold as Glyco Wax S932 (Glyco Products Co.) was employed. The photographic element obtained reproduced one step more than its control.

Example 7 The procedure of Example 1 was followed except that the wax employed was ethylene glycol monostearate, which resulted in a photographic element reproducing two steps more than the corresponding control.

Example 8 The procedure of Example 1 was followed except that an alkyl-stearamide wax (Ceramid, Glyco Products Co.) was employed to produce a coating which reproduced one step more than its control.

It has also been found that vesicular photographic elements nucleated in accordance with my invention may, if desired, be given a further nucleation treatment such as a preflashing treatment of the type described by Contois et al., US. patent application Ser. No. 121,636, filed July 3, 1961, now abandoned. In accordance with this preflashing procedure, a photographic vesicular element is exposed to a uniform prenucleation flash of activating radiation so that the flashed material is capable of prenucleation development to produce an increase of from about 0.03 to about 1.5 density units, and exposing the flashed material within a few minutes of the prenucleation flash to development at a temperature of about 45- 70 C. for a few seconds, such as 5-60 seconds, so that the optical density of the material is increased from about 0.03 to about 1.5 density units above the optical density of the material prior to flashing, and equilibriating the material at ambient conditions for about 12 hours to produce a light-sensitive prenucleated material. This procedure is illustrated in Example 9.

Example 9 A vesicular photographic element prepared in accordance with Example 1 was preflashed with ultraviolet light at 20 foot-candles for 3 seconds, developed for 30 seconds at 60 C. in air to produce a preflash haze of optical density of about 0.8, and was exposed and processed as described in Example 1. The sensitometric properties of this specimen are shown in curve A of FIG. 2. The superior results achieved with this vesicular photographic element is illustrated further by the controls, one of which was prepared as in Example 2 and given a prenucleation flash and development as described above. The sensitometric properties of the element thus obtained are shown in FIG. 2, curve B. Curve C of FIG. 2 is the sensitometric properties of a photographic element ob tained in accordance with Example 2 but which was given no prefiash nucleation and was not nucleated in accord= ance with the invention.

A large number of materials may be employed as a com tinuous binder coating in the vesicular photographic olements of our invention. The useful materials may be broadly described as linear, saturated hydrocarbon polymer chains having essentially no cross linking between the molecules thereof, which polymers are thermoplastic, water-insoluble, non-hygroscopic and non-water swelling, and have a permeability constant for nitrogen within the range of 1x 10* to 1 10- The permeability constant referred to herein and in the appended claims is the number of cubic centimeters of nitrogen transmitted at 30 C. by an area of one square centimeter of polymer in one second when the pressure gradient is one centimeter of mercury per one centimeter of transmission thickness. The useful polymers are thermoplastic and hydrophobic in nature. Particularly useful binders are copolymers of vinylidene chloride and acrylonitrile, which binders may also advantageously comprise poly(methyl methacrylate). The most useful vinylidene chloride-acrylonitrile copolymers are those which contain about 50-80 parts by weight vinylidene chloride and about 50-20 parts by weight acrylonitrile. Poly(vinyl butyral), polyisobutylene, poly(vinyl chloride), polyacrylonitrile, poly(methyl methacrylate) and poly(vinyl acetate) also give satisfac tory results. Other copolymers which may be employed include vinyl chloride and acrylonitrile; styrene and acrylonitrile; acrylonitrile and 1,1-difiuoroethylene vinylidene chloride and acrylic acid; vinyl acetate and vinylidene cyanide; vinyl chloride and acrylic acid; vinyl chlc ride and methyl acrylate; vinylidene chloride and ethyl acrylate; vinyl acetate and vinylidene chloride; vinyl chloride and diethyl maleate; and vinyl chloride and vinyl acetate.

Any wax may be incorporated in the continuous polymeric binder coating which separates as a discontinuous phase in the polymeric binder to provide nucleation in accordance with the invention. These may be, preferably, a hydrogenated oil wax, carnauba wax, hydrogenated castor oil wax, ethylene glycol monostearate wax and an alkyl-stearamide wax. Other suitable waxes include, for example, beeswax, Chinese wax, flat wax, Godang wax, Java wax, insect wax, paraffin wax, montan wax, Ceresin wax, spermaceti wax, and the like. Waxes which are esters derived from long chain monohydric alcohols and long chain acids, high molecular weight hydrocarbons, fatty acids, alcohols and ketones may also be employed. The more useful concentration of wax is from about .5 to 5%, based on the weight of the polymeric binder, concentrations of about 3.7% wax give particularly good results. I

Any light-sensitive gas-forming compound may be employed in the practice of the invention. Highly useful compounds are the diazonium salts and azido compounds, such as the following:

p-diazodiphenylamine sulfate, p-diazodimethylaniline zinc chloride, p-diazo-N-ethyl-N-hydroxyethylaniline zinc chloride, 1-diazo-Z-hydroxynaphthalene-4-sulfonate, p-diethylamino-benzenediazonium chloride,

1-dimethylaminonaphthalene-4-diazonium chloride, ethylene bis(4-azidobenzoate),

azidodiphthalic anhydride,

4-azidoacetophenone,

2, 6-bis (p-azidobenzylidene -4-methylcyclohexanone, 2,4-diazido-6-methylpyrimidine, 4-aZido-6-methyl-1,2,3,3a,

7-pentaazaindene.

Optical sensitizers such as 4-quinolizone,

2-benzoylmethylene-1-methyl-,B-naphthothiazoline, 4-thioquinolizone, 4-anisyl-2,6-diphenylthiapyrylium perchlorate and the like may be used in conjunction with the gas-producing species. The gas releasing compounds may be used in concentration of about 1 to based on the weight of the binder.

The solvents which we employ in the coating compositions may be selected from a wide variety of organic solvents. The principal solvent should be a good solvent for the thermoplastic binder composition employed, and a second solvent is employed which is a poor solvent for the thermoplastic binder, or preferably is one in which the thermoplastic binder is completely insoluble. Typical principal solvents which could be used are tetrohydrofuran, lower ketones such as acetone or methyl ethyl ketone, and esters such as ethyl acetate. Examples of useful second solvents are alcohols having 4 to 6 carbon atoms, such as butanol, isoamyl alcohol, and 2-methyl-1- butanol. The wax employed should be soluble in the second solvent, at least at compounding temperatures (which may, of course, be higher than room temperature). By employing this technique, a continuous coating of the thermoplastic binder is obtained, and a discontinuous phase dispersion of the Wax is uniformly distributed throughout the thermoplastic binder.

Any suitable support may be employed in accordance with the invention, such as poly(ethylene terephthalate), or suitable opaqe supports such as paper having water proofing coatings thereon.

This invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

I claim:

1. In a vesicular film comprising a support having coated thereion a layer comprising a water-insoluble thermoplastic, polymeric binder having a permeabilit; constant for nitrogen ranging from 1X 10- to 1X 10- and a compound which releases nitrogen upon imagewise exposure to radiation, the improvement which comprises adding to said layer a wax in particulate form dispersed as a discontinuous phase throughout said binder to provide nucleation sites for the formation of nitrogen bubbles in said binder.

2. A vesicular film as described in claim 1, wherein the polymeric binder in which said wax is dispersed is selected from the group consisting of (a) copolymers of vinylidene chloride and acrylonitrile containing from about to parts by weight vinylidene chloride and 20 to 50 parts by weight a'c-rylonitrile;

(-b) polyacrylonitrile;

(c) poly(methly methacrylate); and

(d) poly(vinyl acetate); and, wherein the nitrogen releasing compound is selected from the group consisting of diazonium salts and azido compounds.

3. A vesicular film as described in claim 1, wherein the wax is a hydrogenated oil wax.

References Cited UNITED STATES PATENTS 2,703,756 3/1955 Herrick et al 9649 XR 2,748,024 5/1956 Klimkowski et al.

2,807,545 9/1957 Frederick 9675 2,822,271 2/ 1958 Krieger 9675 2,969,015 1/1961 Klimkowski et a1. 9691 XR 3,143,418 8/1964 Priest et a1. 9649 3,202,510 8/ 1965 Hollrnann 9649 XR 3,252,796 5/1966 Lindquist et al'. 9649 3,272,629 9/ 1966 Hills 9675 NORMAN G. TORCHIN, Primary Examiner. C. L. BOWERS, IR., Assistant Examiner. 

1. IN A VESICULAR FILM COMPRISING A SUPPORT HAVING COATED THEREION A LAYER COMPRISING A WATER-INSOLUBLE, THERMOPLASTIC, POLYMERIC BINDER HAVING A PERMEABILITY CONSTANT FOR NITROGEN RANGING FROM 1X10**-11 TO 1X10**-15 AND A COMPOUND WHICH RELEASES NITROGEN UPON IMAGEWISE EXPOSURE TO RADIATION, THE IMPROVEMENT WHICH COMPRISES ADDING TO SAID LAYER A WAX IN PARTICULATE FORM DISPERSED AT A DISCONTINUOUS PHASE THROUGHOUT SAID BINDER TO PROVIDE NUCLEATION SITES FOR THE FORMATION OF NITROGEN BUBBLES IN SAID BINDER. 